fixes #23775; injectdestructors now handles discardable statements (#23780)

fixes #23775

compiler/injectdestructors.nim

@@ -653,7 +653,7 @@ template handleNestedTempl(n, processCall: untyped, willProduceStmt = false,
       for j in 0 ..< it.len-1:
         branch[j] = copyTree(it[j])
       var ofScope = nestedScope(s, it.lastSon)
-      branch[^1] = if it[^1].typ.isEmptyType or willProduceStmt:
+      branch[^1] = if n.typ.isEmptyType or it[^1].typ.isEmptyType or willProduceStmt:
                      processScope(c, ofScope, maybeVoid(it[^1], ofScope))
                    else:
                      processScopeExpr(c, ofScope, it[^1], processCall, tmpFlags)
@@ -701,7 +701,7 @@ template handleNestedTempl(n, processCall: untyped, willProduceStmt = false,
         #Condition needs to be destroyed outside of the condition/branch scope
         branch[0] = p(it[0], c, s, normal)
 
-      branch[^1] = if it[^1].typ.isEmptyType or willProduceStmt:
+      branch[^1] = if n.typ.isEmptyType or it[^1].typ.isEmptyType or willProduceStmt:
                      processScope(c, branchScope, maybeVoid(it[^1], branchScope))
                    else:
                      processScopeExpr(c, branchScope, it[^1], processCall, tmpFlags)

compiler/semstmts.nim

@@ -283,6 +283,7 @@ proc discardCheck(c: PContext, result: PNode, flags: TExprFlags) =
     if implicitlyDiscardable(result):
       var n = newNodeI(nkDiscardStmt, result.info, 1)
       n[0] = result
+      # notes that it doesn't transform nodes into discard statements
     elif result.typ.kind != tyError and c.config.cmd != cmdInteractive:
       if result.typ.kind == tyNone:
         localError(c.config, result.info, "expression has no type: " &

tests/discard/tdiscardable.nim

@@ -140,3 +140,27 @@ block: # issue #14665
         continue
       inc i
   test()
+
+block: # bug #23775
+  proc retInt(): int {.discardable.} =
+    42
+
+  proc retString(): string {.discardable.} =
+    "text"
+
+  type
+    Enum = enum
+      A, B, C, D
+
+  proc doStuff(msg: Enum) =
+    case msg:
+    of A:
+      retString()
+    of B:
+      retInt()
+    of C:
+      discard retString()
+    else:
+      let _ = retString()
+
+  doStuff(C)